Self-centering magnetic suspension

ABSTRACT

A device is provided for magnetically suspending a body which rotates about a vertical axis for centering said body radially with respect to said axis and for maintaining it at a constant height which device comprises a magnet which provides the main suspension force, a round armature fastened to the suspended body under said magnet which armature is provided with a peripheral tapered ridge for producing a radial return force when this armature moves radially with respect to a tapered circular pole piece of said magnet and with a series of disks each interposed between a pair of coils for producing the vertical balancing force as required for keeping the rotating load at a predetermined level.

United States Patent [191 Soglia et al.

[ Dec. 18, 1973 SELF-CENTERING MAGNETIC SUSPENSION Inventors: LucianoSoglia; Aldo Catitti;

Ciampino Di Marino; Giancarlo Sacerdoti, all of Rome, ltaly ComitatoNazionale per IEngergia Nucleare, Rome, ltaly Filed: Feb. 24, 1972 Appl.No.: 228,810

Assignee:

Foreign Application Priority Data Feb. 26, 1971 Italy 48671 A/7l US. Cl.308/10, 335/229 lnt. Cl. Fl6c 39/00 Field of Search 335/216, 229;

References Cited UNlTED STATES PATENTS l0/l958 Dacus 308/10 I 1/1969Chaboseau et al. 308/l0 l2/l97l Kawabe et al. 308/10 X PrimaryExaminerGeorge Harris Attorney-Richards and Geier 57] ABSTRACT A deviceis provided for magnetically suspending a body which rotates about avertical axis for centering said body radially with respect to said axisand for maintaining it at a constant height which device comprises amagnet which provides the main suspension force, a round armaturefastened to the suspended body under said magnet which armature isprovided with a peripheral tapered ridge for producing a radial returnforce when this armature moves radially with respect to a taperedcircular pole piece of said magnet and with a series of disks eachinterposed between a pair of coils for producing the vertical balancingforce as required for keeping the rotating load at a predeterminedlevel.

7 Claims, 4 Drawing Figures PATENTED DEC 18 I975 SHEET 1 OF 4SELF-CENTERING MAGNETIC SUSPENSION The object of this invention is anapparatus for magnetically suspending and self-centering a body whichrotates about a vertical axis.

The use is already known of permanent magnets for suspending a rotatingbody although a stable vertical position of the body is not ensured bythe devices so far disclosed to this purpose. The use also ofelectrodynamic fields is known as a means for suspending rotating bodieswhich fields are produced by alternate current coils which act on metalmasses attached to the suspended object. Usually the suspension devicesso far produced are based either on one or the other of the aboveprinciples. However, as known, the permanent magnet suspension, althoughoffering the advantage of a compact structure, has the drawback that thesuspended body is not in a state of stable vertical equilibrium, in facta stable equilibrium is reached in that case only when the body weightand the magnet force acting upon the body are balanced, the state ofbalance being attained for one only of the reciprocal positions of thetwo system components, that is the body and the magnet. The system thenis considered to be instable.

On the other side the electrodynamic suspension, while permitting acontinuous adjustment of the suspending force, suffers from the drawbackof requiring an amount power which is quite considerable when comparedto the suspended body weight and of being exceedingly large. It alsodoes not display any effective radial centering action.

It is therefore an object of this invention to provide a device whereinthe advantages are combined and the drawbacks are attenuated of the twomethods and which is adapted for supplying a self-centering action onthe suspended body.

According to this invention the electrodynamic force exerted by stackedcoils on electroconductive metal masses fastened to a suspended body isconbined with the force exerted by a permanent magnet on a ferromagneticarmature fastened to the same body; said coils being fed with alternatecurrent.

The magnitudes of the above forces are determined in such a way that thepermanent magnet sustains the greater part of the body weight while thecoils are given the task of maintaining the body at its equilibriumposition and of supplying that part of the suspension force which is notprovided by the permanent magnet. In other words, the force supplied bythe coils automatically concurs with or opposes to the force supplied bythe magnet depending on whether a concurrent or opposed force isrequired by the system for reaching a predetermined equilibriumposition. A particular configuration of the magnet armature and polepieces permits the centering of the suspended load and of the armaturewith respect to the magnet.

It is to be noted that there is no mechanical contact between thesuspended load and the generating means of the suspension forces whenthe equilibrium position is attained, a predetermined space being leftbetween them which will be referred to as air gap although it can alsobe occupied by a fluid other than air.

A first advantage of this invention is that the operating cost of thesuspension is reduced with respect to a suspension operated by coilsonly, and this because,-as already mentioned, the suspension force ismainly supplied by the magnet while the coils provide that force onlywhich is required for compensating the unbalance between the magnetforce and the body weight in order to maintain the latter at itsequilibrium position.

A further advantage of the invention is that the suspended body isautomatically centered'by virtue of the geometrical configuration of themechanical components of the magnetic circuit including the permanentmagnet and particularly of the confronting surfaces of the magnet and ofits armature.

Another advantage of the suspension device of this invention is that abody can be suspended thereby in such a way that the body can be rotatedabout the suspension axis without any mechanical contact between thestationary and the rotating members and therefore without any mechanicalfriction between them.

A further advantage of this device consists on its simple structurewhereby it is definitely distinguished among the similar suspension sofar disclosed.

Other advantages will become apparent from the following description anddrawings:

FIG. 1 shows an axial section of the device of this invention;

FIG. 2 is an axial section of a variant to the ambodiment of FIG. 1;

FIG. 3 shows an axial section of another variant of the device of thisinvention;

FIG. 4 is the same section of FIG. 1 wherein the magnet polarities areindicated.

With reference to FIG. 1 the device of this invention comprises thefollowing essential components a permanent magnet 2 of circular formeither annular or solid with vertical axis and flat horizontal bases ofwhich the upper one is larger than the lower;

a magnet support 1 made of ferromagnetic material with cylindrical formand horizontal upper and lower bases the lower base having generally thesame surface of the upper base of magnet 2 and being securely bondedthereto. The upper portion of said support extends radially that ishorizontally and then downwardly to reach with its terminal tapered edgethe level of the lower face of said magnet. In this way a toroidal spaceis defined between said descending wall or skirt lb and the innercylinder consisting of the magnet .and the overlying support portion;

an armature 3 by which the magnetic circuit generated by magnet 2 isclosed which armature is diskshaped, coaxial with said support inoperation and provided with circular projections ll, 12 on its faceconfronting the bottom horizontal surfaces 13, 14 of magnet 2 and skirtlb with an air gap between them; the reciprocally confronting faceshaving substantially the same surface;

a cylindrical hub 15 extending downwards from said armature 3, theuseful load 16 being suspended from the bottom end of said hub;

one or more metal disks keyed on said hub 15;

two or more stacked electric coils 4 vertically spaced at a distancefrom one another large enough for receiving said metal disk 5therebetween which coils are fastened to support 1 through a casing 20of non magnetic material;

two annular shields 6 fastened to coils 4, which shields extendhorizontally to cover those surfaces of coils 4 which are not facingbody 5.

Magnet 2 and support 1 with the related portions la and lb along withcoils 4 are all mechanically connected to one the others and to anexternal stationary support not shown.

The major portion of the force for suspending the load attached toarmature 3 including the useful load 16 is supplied by the magnetic fluxthrough the pairs of pole pieces 12,14 and ll, 13 and through air gap 10therebetween.

Because the reciprocally facing surfaces of these pole pieces 11 and 13are very narrow, a centering force is provided by them. In fact anyradial displacement of armature 3 is counteracted by the magnetic forcewhich tends to keep said piece poles in alignment. In fact as shown inFIG. 4, the magnetic circuit generated by magnet 2 and extending alongthe outer skirt of support 1 and along air gap 10a and armature 3, isstrongly counter acted in the region of air gap 10 due to the smallextension of the reciprocally facing surfaces across the gap and as aconsequence a strong return action is produced when said surfaces areradially displaced from alignment.

Coils 4 have an annular form and a current is circulated through themwhich generates a magnetic field substantially perpendicular to thedisklike body 5. The radial section of disk 5 may be rectangular andthickened towards the axis in order to form a stronger root section 17to withstand the centrifugal force when the suspended load is rotated athigh speed.

The surfaces of disk 5 and of shields 6 facing coils 4 are preferablyparallel to each other.

Disk 5 and shields 6 are made of a good electroductive material, forinstance aluminium, copper etc. Support '1 along with its portions 10and lb and armature .3 are made of ferromagnetic material; hub may be ofany material with mechanical properties as required for meeting theexpected operating stresses.

According to a variant of the embodiment illustrated in'FIG. 1, twodisks 5, as shown in FIG. 2, are mounted on the armature extension orhub 15. The two disks are interposed between three coils 4 withreciprocally facing horizontal surfaces. Obviously the number of disksSand of coils 4 may be larger than three and four respectively when alarger balancing force is required by disks 5 on coils 4.

Coils 4 are connected in series and are excited by means of alternatecurrent with a frequency in the range from 100 to 5000 Herz.

The thickness of disks 5 and shields 6 will be dimensioned so as toavoid that said disks and shields be traversed by the magnetic linesgenerated by coils 4. In fact said lines should penetrate a portion onlyof the total thickness of said disks and shields so that the eddycurrents generated in said elements be such as to produce repulsivefields that is such fields that are a mirror image of the fieldsproduced by the current flowing through the coils.

The repulsive electrodynamic forces exerted by coils 4 on disks 5 tendto increase when the distance between the coil and one of the facingsurfaces of conducting material decreases. As a consequence the systemin which disks 5 are incorporated including the suspended loadoscillates about a stable equalibrium position. In other words, when theload to be suspended moves in the direction of arrow 9 of FIG. 1, space7 becomes shallower and correspondingly space 6 becomes deeper. However,as a consequence of this upward movement, the repulsive force of coil 4aon disk 5 is increased with respect to the force exerted by coil 4b onthe same disk wherebya stabilizing action is obtained on disk 5 andconsequently on the suspended load. By means of shields 6 which preventany dispersion of the magnetic field produced by coils 4 the efiiciencyof the same coils is increased, that is the force exerted by the coilson disks 5 is increased without any increase of the exciting power.

Magnet 2 can be made of any magnetic material; however the performancesof theapparatus will be strongly influenced by the magnetic propertiesof this material.

In those cases when the suspension force supplied by the magnet is to beadjusted without changing the depth of air gaps 10,10a an additionaladjustableair gap can be provided as shown by FIG. 3.

As shown in this figure, the central portion la of support 1 of FIG. 1is replaced by a ferromagnetic plug 18 which is threaded on its outersurface for engaging a corresponding threaded bore provided at thecenter of the upper portion of support I. In this manner an additionalair gap 19 is inserted in the magnetic circuit of magnet 2, whichcircuit therefore comprises now in addition to the magnet the followingcomponents:

In this case, permanent magnet 2 is sustained by support 21 which ismade of non magnetic material. Support 21 maintains unchanged thereciprocal position of magnet 2, support 1 and casing 20.

It is clearly understood that air gap 19 can be made to interrupt themagnetic circuit at locations other than that shown in FIG. 3, forinstance along skirt lb, and that more than one adjustable air gaps maybe provided.

According to a second embodiment of this invention, not shown in thefigures, the permanent magnet of the suspension device has the form of aring coaxial with support 1, which ring occupies the lower portion ofskirt lb of the same support and has the same cross section of it. Saidmagnet ring, according to a first variant, is fastened to the rest ofthe skirt and according to second variant it is fastened to stationarysupport 20. Still according to this second variant, an air gap isprovided between the top face of the ring magnet and the bottom face ofthe remaining skirt; in addition, the latter is con-jnected to thecentral portion 1a of support 1 by means of a threading which isprovided on any couple of adjoining cylindrical surfaces coaxial withsaid outer and inner support portions. In this way said air gap andconsequently the force exerted by the magnet on armature 3 can beadjusted without modifying the air gap 10 between the body in which themagnet is incorporated and armature 3.

It is to be observed that in FIGS. 1, 2, 3 the central portions ofmagnet support 1, armature 3 and hub 15 are shown as provided withaligned central bores to indicate that the suspended body is madeaccessible through the suspension device with the purpose of introducinginto the body when this is, for instance, a ves- -sel sundry solidobjects or liquids.

What is claimed is:

l. A device for suspending a load by means of magnetic forces at apredetermined level and for centering it with respect to a vertical axisand keeping it mechanically separated in operation from the surroundingstructure by a space which maybe filled with a fluid, which devicecomprises a stationary circular cylindrical body with vertical axis andhorizontal bases in which body a toroidal recess is provided extendingfrom the bottom base upward for a distance shorter than the body heightwhereby a cup-like shape is obtained of said body with a centralcylindrical boss and outer cylindrical skirt, the lower ends of saidboss and skirt being substantially at the same level, said skirtterminating with a downwardly pointing tapered edge; said cylindricalbody being made of ferromagnetic material; a permanent magnet beingincorporated therewith to provide a magnetic field of which the polepieces are the circular tapered edge of said skirt and the bottom end ofsaid boss; which device comprises a disk shaped armature fastened tosaid load and provided on its upper surface with a central projectionaligned with said cylindrical boss and having substantially the samediameter and with a peripheral tapered ridge aligned with the taperededge of said skirt; the upper surface of said central projection andperipheral ridge being separated in operation from the confrontingsurface of said cylindrical bell-shaped body by an air gap; which devicecomprises also at least one disk-shaped horizontal body of electricityconducting material coaxial with said armature .and fastened thereto;each disk-shaped body being interposed between two annular horizontalcoils mounted on a stationary support and excited by an external powersource; the force for suspending the weight of load and of thestructural components connected thereto being provided for a majorportion by said permanent magnet while the difference between saidweight and the magnet force is provided by said coils.

2. A device as claimed in claim 1, in which device said electric coilsof annular form are stacked and coaxial one to the others and saidelectricity conducting metal bodies are circular and flat each of thembeing interposed between two of said coils; a separation space beingleft between the body and the adjacent coils whereby eddy currents areinduced on said conducting bodies when said coils are energized withelectric current; said annature being provided on its face confrontingthe permanent magnet with circular concentric projections which arealigned with the inner and outer circular pole pieces of the magnet andrelated support skirt; said device being further provided with twocircular flat shields made of electricity conducting material which areplaced above and below the coils stack with the purpose of preventingthe magnetic flux generated by the coils from invading the spacesurrounding the assembly of the conducting bodies and of the coils.

3. A suspension device as claimed in claim 1, wherein said permanentmagnet has the form of a right circular cylinder with vertical axis andstrongly tapered at its lower portion, while its top base joins thebottom end of a ferromagnetic support which also has the form of a rightcircular cylinder and preferably the same cross section as the top baseof the magnet, which support at its upper end extends horizontally for adistance and then vertically downwards to form a skirt which reaches thelevel of the bottom end of the magnet with a strongly tapered edgewhereby an annular downwardly open space is defined between saidcylindrical portion and said skirt portion of said support; in whichdevice said armature is in the form of a disk from the upper surface ofwhich a central circular boss and a tapered peripheral ridge projectupwards to face respectively the bottom base of the magnet and the edgeof said support skirt; said boss and ridge being separated in operationfrom the corresponding surfaces of said magnet and skirt by an air gap.

4. A device as claimed in claim 3 wherein said central cylindricalportion of said support is connected to the horizontally extendingportion of the same support by a screw thread provided onthe sidesurface of said cylindrical portion which screw thread engages acorresponding screw threading of a central bore provided through saidhorizontal portion a cuplike member being provided for firmly connectingthe latter to said horizontal support portion, whereby the bottom end ofthe support cylindrical portion can be adjustably moved towards and awayfrom the top magnet base and the strength of the magnetic flux can beadjusted without changing the relative positions of the magnet andarmature.

5. A device for suspending a load and maintaining it centered withrespect to a vertical axis, as claimed in claim 1, wherein saidpermanent magnet has the form of a ring coaxial with said body offerromagnetic material which ring occupies the lower portion of theouter wall of said body and is fastened to the rest of the same wall;its cross section being trapezium-shaped with a horizontal side equal tothe wall thickness and the opposed side very short and substantiallyequal to the width of the confronting top face of the armatureperipheral ridge.

6. A device as claimed in claim 5 wherein said permanent magnet has theform of a ring coaxial with said body of ferromagnetic material whichring occupies the lower portion of the outer wall of said body andseparated by an adjustable air gap therefrom said magnet being fastenedto a stationary support while the rest of said outer wall can be movedup and down with respect to the stationary central portion of saidferromagnetic body by means of the screw threaded engagement betweenthem.

7. A device as claimed in claim 1 wherein a cylindrical bore coaxialwith said cylindrical body and in operation with said armature and saiddisk-shaped bodies is provided for giving access to the suspended loadfrom the top of the suspension device.

1. A device for suspending a load by means of magnetic forces at apredetermined level and for centering it with respect to a vertical axisand keeping it mechanically separated in operation from the surroundingstructure by a space which may be filled with a fluid, which devicecomprises a stationary circular cylindrical body with vertical axis andhorizontal bases in which body a toroidal recess is provided extendingfrom the bottom base upward for a distance shorter than the body heightwhereby a cuplike shape is obtained of said body with a centralcylindrical boss and outer cylindrical skirt, the lower ends of saidboss and skirt being substantially at the same level, said skirtterminating with a downwardly pointing tapered edge; said cylindricalbody being made of ferromagnetic material; a permanent magnet beingincorporated therewith to provide a magnetic field of which the polepieces are the circular tapered edge of said skirt and the bottom end ofsaid boss; which device comprises a disk shaped armature fastened tosaid load and provided on its upper surface with a central projectionaligned with said cylindrical boss and having substantially the samediameter and with a peripheral tapered ridge aligned with the taperededge of said skirt; the upper surface of said central projection andperipheral ridge being separated in operation from the confrontingsurface of said cylindrical bell-shaped body by an air gap; which devicecomprises aLso at least one disk-shaped horizontal body of electricityconducting material coaxial with said armature and fastened thereto;each disk-shaped body being interposed between two annular horizontalcoils mounted on a stationary support and excited by an external powersource; the force for suspending the weight of load and of thestructural components connected thereto being provided for a majorportion by said permanent magnet while the difference between saidweight and the magnet force is provided by said coils.
 2. A device asclaimed in claim 1, in which device said electric coils of annular formare stacked and coaxial one to the others and said electricityconducting metal bodies are circular and flat each of them beinginterposed between two of said coils; a separation space being leftbetween the body and the adjacent coils whereby eddy currents areinduced on said conducting bodies when said coils are energized withelectric current; said armature being provided on its face confrontingthe permanent magnet with circular concentric projections which arealigned with the inner and outer circular pole pieces of the magnet andrelated support skirt; said device being further provided with twocircular flat shields made of electricity conducting material which areplaced above and below the coils stack with the purpose of preventingthe magnetic flux generated by the coils from invading the spacesurrounding the assembly of the conducting bodies and of the coils.
 3. Asuspension device as claimed in claim 1, wherein said permanent magnethas the form of a right circular cylinder with vertical axis andstrongly tapered at its lower portion, while its top base joins thebottom end of a ferromagnetic support which also has the form of a rightcircular cylinder and preferably the same cross section as the top baseof the magnet, which support at its upper end extends horizontally for adistance and then vertically downwards to form a skirt which reaches thelevel of the bottom end of the magnet with a strongly tapered edgewhereby an annular downwardly open space is defined between saidcylindrical portion and said skirt portion of said support; in whichdevice said armature is in the form of a disk from the upper surface ofwhich a central circular boss and a tapered peripheral ridge projectupwards to face respectively the bottom base of the magnet and the edgeof said support skirt; said boss and ridge being separated in operationfrom the corresponding surfaces of said magnet and skirt by an air gap.4. A device as claimed in claim 3 wherein said central cylindricalportion of said support is connected to the horizontally extendingportion of the same support by a screw thread provided on the sidesurface of said cylindrical portion which screw thread engages acorresponding screw threading of a central bore provided through saidhorizontal portion a cuplike member being provided for firmly connectingthe latter to said horizontal support portion, whereby the bottom end ofthe support cylindrical portion can be adjustably moved towards and awayfrom the top magnet base and the strength of the magnetic flux can beadjusted without changing the relative positions of the magnet andarmature.
 5. A device for suspending a load and maintaining it centeredwith respect to a vertical axis, as claimed in claim 1, wherein saidpermanent magnet has the form of a ring coaxial with said body offerromagnetic material which ring occupies the lower portion of theouter wall of said body and is fastened to the rest of the same wall;its cross section being trapezium-shaped with a horizontal side equal tothe wall thickness and the opposed side very short and substantiallyequal to the width of the confronting top face of the armatureperipheral ridge.
 6. A device as claimed in claim 5 wherein saidpermanent magnet has the form of a ring coaxial with said body offerromagnetic material which ring occupies the lower portion of theouter wall of said body and separated by aN adjustable air gap therefromsaid magnet being fastened to a stationary support while the rest ofsaid outer wall can be moved up and down with respect to the stationarycentral portion of said ferromagnetic body by means of the screwthreaded engagement between them.
 7. A device as claimed in claim 1wherein a cylindrical bore coaxial with said cylindrical body and inoperation with said armature and said disk-shaped bodies is provided forgiving access to the suspended load from the top of the suspensiondevice.